This invention relates to reciprocating internal combustion engines, such as diesel, gasoline or natural gas powered engines, and is more specifically directed to an internal combustion engine whose major parts, including cylinder block and pistons, are made of a high performance synthetic resin material.
An effort has been made to reduce the design weight of automotive engines, or other engines, and at the same time to increase efficiency and longevity. To this end, synthetic materials have been used in such engine parts as oil pans, valve covers, gear covers, cranks, and some internal parts such as rocker arms and connecting rods. One composite engine block, in which an outer shell is formed of a synthetic material, with cylinder sleeves formed of cast iron and with metal pistons, is described in U.S. Pat. Nos. 4,930,470. 4,440,069 discusses a composite piston for an internal combustion engine, in which the piston has a metal head or crown, and a skirt formed of a thermoplastic material, e.g., an amide-imide polymer with a high melting temperature. Polymer structures for use in internal combustion engines, such as for valve covers, composite connecting rods, and composite rocker arms, are discussed in the literature, e.g., U.S. Pats. Nos. 5,375,569; 4,726,334; and 4,438,738.
To date, even though durable synthetic materials are available, no one has previously proposed an internal combustion engine in which the components that constitute the combustion chamber itself, i.e., the piston and the cylinder walls, are formed of one of these high performance synthetic resin materials.
Several suitable high performance composite resins exist, which can withstand the extreme high temperatures and pressures of combustion of hydrocarbon fuels, and which have advantages of strength and light weight. These can include PEEK (polyether ether ketone), PTI (thermoplastic polyimide), PBI (polybenzimidazole), and PAI (polyamide-imide). However, with a traditional round-profile cylinder and piston construction, it is difficult to provide adequate lubrication and sealing.
Non-round profile piston/cylinder design in a reciprocating machine has been proposed for some applications. U.S. Pat. No. 1,761,123 describes a rectangular piston and rectangular cylinder, in which there is a cage of rollers in the space between the piston and cylinder, and the bearing cage is free to travel up and down during the piston stroke. This structure was proposed for use in a pump or compressor. However, to date, no one has proposed a polygonal profile design for a piston and cylinder in an internal combustion engine, nor associated with any device in which the piston and cylinder walls are formed of a synthetic or composite resin.